Polystyrene (PS)/aluminum hydroxide (Al(OH)(3)) composite particles were successfully prepared by the sol-gel process of aluminum isopropoxide (Al(OPr')(3)) in a hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) using ammonium hydroxide (NH4OH) as a catalyst in the presence of PS seed. Transmission electron microscopy observation of ultrathin cross sections of the composite particles revealed that the composite particles had a core-shell morphology consisting of a PS core and a Al(OH)(3) shell having high crystallinity. nucleated Al(OH)(3) could be reduced by dropwise addition of NH4OH. Moreover, PS/eta-Al2O3 successfully prepared by heat treatment of PS/Al(OH)(3) at 300 degrees C in N-2 atmosphere, which is temperature of PS.